Offset electrode

ABSTRACT

An electrode including a non-conductive substrate having a top surface and at least one channel extending therethrough, an electrically conductive trace material positioned adjacent a portion of the top surface of the non-conductive substrate and extending through the channel, and adapted for electrically coupling to a power source, and a second electrically conductive material that is inert or more corrosion resistant than the trace material. The second material is positioned adjacent to and entirely covering a top surface of the trace material. The electrode further includes a conductive hydrogel laterally offset from the trace material, the hydrogel may be positioned adjacent to a portion of a top surface of the second electrically conductive material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/605,409, filed Oct. 26, 2009, which is hereinincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the construction ofelectrodes, and more particularly to electrodes used to deliverelectrical energy to the skin having a design and construction that isparticularly suited to resist corrosion.

2. Description of Related Art

For many years electrodes have been used to deliver electrical energy tothe skin for various purposes such as for pain management and musclestimulation. When used for transdermal applications, stimulationelectrodes usually require the use of a conductive liquid or gel, oftencalled a “hydrogel”, to provide a continuous and efficient conductivepath between the current source and the skin. Conductive hydrogelstypically contain salt, and as such can be corrosive to common electrodetrace materials, which adversely affects the performance of theelectrode. Thus, when designing integrated electrodes for transdermalstimulation, in order for such devices to be commercially viable theymust have a sufficiently long shelf life, which requires a design thatminimizes or eliminates the ability of the hydrogel to migrate and reachthe trace elements over time.

One known method for “isolating” a hydrogel from copper traces in anelectrode is to cover the copper with an electrically conductive, butmore corrosion resistant or inert substance, such as gold. An example ofthis is illustrated in FIG. 1, where electrode 100 includes anon-conductive substrate 101 (i.e., fiberglass) having an aperture 102through which a conductive trace material or conductive pad 103 passesand is subsequently electrically coupled to an integrated circuit 120 orthe like that provides power to the electrode. The conductive tracematerial is also applied across a top surface of the non-conductivesubstrate. A gold or nickel/gold layer 104 is then applied via the wellestablished ENIG (electroless nickel immersion gold) process over theconductive trace element so as to isolate the trace material from thehydrogel 105 as described above. Gold is well known to be a conductive,but inert material, but is also well known to be expensive. Further,although a gold layer theoretically prevents corrosion, in realityvariations and/or imperfection in manufacturing processes, particularlyin thin film techniques, result in varying degrees of corrosion overtime, which presents challenges when designing products for long-termuse and/or when long term shelf-life is needed.

Others have been known to incorporate further additional conductivelayers between the copper trace material and the hydrogel in an effortto prevent or minimize corrosion. This solution has been used by AlzaCorporation of Mountain View, Calif., and an example of such solution isillustrated in FIG. 2. The non-conductive substrate 201 of the electrode200 includes a conductive copper trace material 203 on its top surface.Deposited on top of the trace material 203 is one or more additionalconductive, but inert or more corrosion resistant layers such as anelectrically conductive tape 206 and a silver foil 207. When theelectrode is placed on the skin of a patient, the hydrogel 105 is placedbetween the skin and the additional conductive players. Althoughincorporation of additional layers between the copper and hydrogel doesprovide added corrosion protection, it also increases the material andassembly costs for the electrode.

Accordingly, what is needed is an improved electrode design that hasreduced material and assembly costs, yet provides sufficient corrosionresistance for use as a commercial, transdermal electrode assembly.

SUMMARY OF THE INVENTION

The present invention provides an electrode having a non-conductivesubstrate having a top surface and at least one channel extendingtherethrough, an electrically conductive trace material positionedadjacent at least a portion of the top surface of the non-conductivesubstrate and extending through the channel, and being adapted to beelectrically coupled to a power source. The electrode further includes asecond electrically conductive material that is inert or more corrosionresistant than the trace material, and that is positioned adjacent toand entirely covering a top surface of the trace material. A hydrogel islaterally offset from the trace material. The hydrogel may be positionedadjacent to a portion of a top surface of the. second electricallyconductive material.

The top surface of the non-conductive substrate may include a recessedportion, and the at least one channel may be positioned within therecessed portion. In yet another embodiment, the electrically conductivetrace material is positioned entirely within the recessed portion, andthe second electrically conductive material may also be positionedentirely within the recessed portion.

In one embodiment, the trace material is made of copper, and in yetanother embodiment, the second electrically conductive material is madeof gold/nickel. Further, the third electrically conductive material maybe made of silver.

In another alternate embodiment, the electrode may include a foammaterial positioned adjacent to at least a portion of a top surface ofthe third electrically conductive material so as to substantiallysurround the hydrogel.

Also provided is an electrode including a non-conductive substratehaving a top surface and a bottom surface and at least one channelextending therethrough, where the non-conductive substrate is made of aflexible material. The electrode further includes a copper tracematerial positioned adjacent at least a portion of the top surface ofthe non-conductive substrate and extending through the channel, with thetrace material being adapted to be electrically coupled to an electrodepower source. The electrode further includes a second conductivematerial made of gold or gold/nickel, and positioned adjacent so as tocover a top surface of the trace material; and a conductive hydrogelbeing laterally offset from the trace material. The hydrogel may bepositioned adjacent to and covering at least a portion of a top surfaceof the second conductive material.

In one embodiment, the electrode further includes a foam materialsubstantially surrounding the hydrogel yet leaving a top surface of thehydrogel exposed.

In yet another embodiment, the top surface of the non-conductivesubstrate includes a recessed portion, and the at least one channel ispositioned within the recessed portion.

In alternate embodiments, the electrically conductive trace material ispositioned entirely within the recessed portion, and the secondelectrically conductive material may also be positioned entirely withinthe recessed portion.

These and other features and advantages of the present invention willbecome apparent from the following more detailed description, when takenin conjunction with the accompanying drawings which illustrate, by wayof example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1 and 2 illustrate known prior art electrode assemblies;

FIG. 3 illustrates one embodiment of an electrode according to thepresent invention; and

FIG. 4 illustrates yet another embodiment of an electrode according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Before explaining the present invention in detail, it should be notedthat the invention is not limited in its application or use to thedetails of construction and arrangement of parts illustrated in theaccompanying drawings and description. The illustrative embodiments ofthe invention may be implemented or incorporated in other embodiments,variations and modifications, and may be practiced or carried out invarious ways. For example, although the present invention is describedin detail in relation to electrodes for transdermal neurostimulation, itis to be understood that such electrodes have various other uses andapplications as will be apparent to those skilled in the art.

FIG. 3 illustrates one exemplary embodiment of an electrode according tothe present invention. The electrode 500 includes a non-conductivesubstrate 501, which may be comprised of any well known material such asFR4 fiberglass or polyamide. The substrate has a lateral width w, a topsurface 510 including a recessed portion 512 that surrounds an aperture502 extending therethrough. Positioned through the aperture 502 andacross the recessed portion 512 of the top surface 510 is anelectrically conductive trace material 503 such as copper. As usedherein, the term “trace material” is intended to mean that which iscapable of conducting electricity to form a circuit when electroniccomponents are soldered to it, and may include any type of traceelement/material, conductive pads, or the like. The trace material iselectrically coupled to a power source (not shown) in a well knownmanner. This embodiment further includes a second electricallyconductive, but inert or more corrosion resistant material 515,preferably gold or gold/nickel, that is applied via a well establishENIG process so that it both entirely covers the top surface 514 of thetrace material 503, but also passes through smaller aperture 502 aextending through the trace material as shown. Positioned adjacent to atleast a portion of the first surface 510 of the non-conductive substrateand also adjacent to the top surface 518 of the second electricallyconductive material 515, and otherwise covering the first electricallyconductive material, is a third layer of electrically conductive, butinert or more corrosion resistant material 513. Material 513 covers awidth x such that it extends beyond the top surface of the tracematerial 503 on all respective sides as exemplified by p1 and p2 on FIG.3. In a preferred embodiment, the third conductive material 513 issilver ink that can be directly applied by known screen-printingtechniques.

The hydrogel 505 is applied across a portion of the top surface 516 ofthird electrically conductive material 513. As illustrated in theembodiment of FIG. 3, the trace material 503 and the hydrogel 505 arelaterally offset from one another by distance p2. By “laterally offset”what is meant is that no portion of the hydrogel is positioned directlyabove any portion of the trace material. In this manner, should there beany imperfections during application of material 513 and 515, thehydrogel is less likely to reach the trace material thru migration thanit would if positioned directly over the trace material.

Finally, a preferred embodiment of the present invention is illustratedin FIG. 4, which is similar to the embodiment of FIG. 3, butincorporates additional features. The electrode 600 of FIG. 4 alsoillustrates an additional layer of a foam 601 or the like, such aspolyurethane, that is laminated directly onto both the exposed topsurface 510 of the non-conductive substrate, and also to the top surface516 of the silver layer 513 to thereby substantially surround thehydrogel 505 while leaving a top surface 610 of the hydrogel exposed. Inthis manner, the laterally offset hydrogel is prevented from migratinglaterally, further reducing the chance of the hydrogel contacting thetrace element.

Short term stability tests were carried out on electrodes constructed asshown in FIG. 1 as well as electrodes constructed as shown in FIG. 4.With regard to those constructed as shown in FIG. 1, these electrodeswere found to be functional, but with an “unstable” design highlysubject to corrosion as a result of manufacturing variability in thedeposition of inert material intended to keep the hydrogel andunderlying copper separated. Twenty electrodes enclosed in heat sealedfoil pouches were tested in an accelerated aging environment chamber at50 degrees Celsius. Within 3 days all electrodes exhibited greendiscoloration indicative of corrosion. When the same stability testswere performed on twenty electrodes constructed as shown in FIG. 4, nocorrosion was visible after 34 days. The results of these stabilitytests demonstrate significant improvement in the electrodes of thepresent invention.

In one preferred embodiment, the electrodes described herein may beincorporated within a transdermal neurostimulation patch of the typeillustrated and described in U.S. patent application Ser. No.11/941,508, filed on Nov. 16, 2007, which is hereby incorporated byreference in its entirety.

While the foregoing describes specific embodiments of the presentinvention, other and further embodiments may be devised withoutdeparting from the basic scope thereof. As such, the scope of thepresent invention is to be limited only as set forth in the appendedclaims.

What is claimed is:
 1. An electrode comprising: a non-conductivesubstrate having a top surface and a channel extending therethrough; thetop surface of the non-conductive substrate having a recessed portiondefined therein; an electrically conductive trace material positionedadjacent at least a portion of the top surface of the non-conductivesubstrate entirely within said recessed portion and said channel; andthe electrically conductive trace material extending through saidchannel, and being adapted to be electrically coupled to a power source;and a second electrically conductive material that is inert or morecorrosion resistant than the trace material, the second electricallyconductive material being positioned adjacent to and entirely covering atop surface of the trace material; the second electrically conductivematerial being positioned entirely within said recessed portion and thechannel; wherein at least a portion of an outer surface of each of theelectrically conductive trace material and the second electricallyconductive material is in direct physical contact with thenon-conductive substrate.
 2. The electrode according to claim 1, whereinthe trace material is comprised of copper.
 3. The electrode according toclaim 1, wherein the second electrically conductive material iscomprised of gold or gold/nickel.
 4. The electrode according to claim 1,wherein each of the electrically conductive trace material and thesecond electrically conductive material extend from said recessedportion through said channel to a bottom surface of the non-conductivesubstrate.
 5. The electrode according to claim 1, wherein theelectrically conductive trace material encircles the second electricallyconductive material in a portion of said channel extending from saidrecessed portion to a bottom surface of the non-conductive substrate,the electrically conductive trace material does not extend to the topsurface of the non-conductive substrate.
 6. An electrode comprising; anon-conductive substrate having a top surface and a bottom surface and achannel extending therethrough, the non-conductive substrate beingcomprised of a flexible material; the top surface of the non-conductivesubstrate haying a recessed portion defined therein; a copper tracematerial positioned adjacent at least a portion of the top surface ofthe non-conductive substrate entirely within said recessed portion andthe channel; and the electrically conductive trace material extendingthrough said channel, said trace material being adapted to beelectrically coupled to an electrode power source; and a secondconductive material comprised of gold or gold/nickel, and positionedadjacent to and covering a top surface of said trace material; and thesecond electrically conductive material being positioned entirely withinsaid recessed portion and the channel; wherein at least a portion of anouter surface of each of the electrically conductive trace material andthe second electrically conductive material is in direct physicalcontact with the non-conductive substrate.
 7. The electrode according toclaim 6, wherein each of the electrically conductive trace material andthe second electrically conductive material extend from said recessedportion through said channel to a bottom surface of the non-conductivesubstrate.
 8. The electrode according to claim 6, wherein theelectrically conductive trace material, encircles the secondelectrically conductive material in a portion of said channel extendingfrom said recessed portion to a bottom surface of the non-conductivesubstrate, the electrically conductive trace material does not extend tothe top surface of the non-conductive substrate.